1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and particularly to a semiconductor memory apparatus such as a memory circuit.
2. Description of Related Art
On a semiconductor memory apparatus of a related art, a plurality of memory cells are arranged in a matrix. Selecting addresses in row and column direction on the semiconductor memory apparatus reads or writes a memory cell of any position. On a semiconductor memory, a word line of a specified row direction is activated so as to read data on a bit line corresponding to a specified column or to write data to the specified bit line.
As disclosed in Japanese Unexamined Patent Publication No. 2000-133777, there is a known method when placing memory cells of the semiconductor memory apparatus in a matrix, of which placing a decoder and a word line driver to drive word line on the central part of the memory cells. Placing a row decoder and a word line driver on the central part reduces the length of a word line to half and also enables a semiconductor memory to speed up.
However when placing memory cells in this manner, a word line driver to activate a word line must be set up on the left and right sides, thereby requiring a large area in word line driver layout. To reduce the area of the word line driver, a common word line driver may be used to drive both sides of the word lines.
However in a case for example where a memory cell is a DRAM, a pitch between word lines on a memory cell part is too narrow for arranging a row decoder part and a common word line driver in accordance with the pitch on the memory cell part. Consequently it does not leave a sufficient space in the layout of the row decoder part, thereby making it impossible to arrange a word line to pass through the row decoder part unless extending the pitch between word lines or adding a new wiring layer. Accordingly in the related art, a row decoder is placed on the central part and word line drivers on the left and right sides, and then extending the word lines towards left and right direction. However if a pitch between word lines is narrow, a word line driver has to be arranged widely in a word line direction because of the pitch, thus increasing the row decoder area relatively and also preventing from reducing the area of the overall memory cell part.